Dynamic strain pickup



Feb. 3, 1948. v w, RAMBERG l 2,435,254

DYNAMIC STRAIN PICK-UP Filed Sept. 25, 1945 www Waller Ramberg'.

f (Lw LW Patented Feb. 3, 13948 DYNAMIC STRAIN PICKUP Walter Bamberg,Chevy Chase, Md.

Application September 25, 1945, Serial No. 618,597

3 Claims. (Cl. 20L-52) (Granted under the act of March 3, 1883, asamended April 30, 1928; 370 0. G. 757) My invention relates generally tapparatus f014 detecting vibrational displacements, and moreparticularly to the pick-up component therefor.

The principal advantage of this pick-up over presently availablepick-ups is ,its exceptionally large voltage variations for smallvibrational displacements. The output is ample to operate high frequencyrecording galvanometers directly without the complication of highfrequency oscillators and amplifiers.

A useful application would be the recording of vibration on aircraft inflight. Another promising application is in resonance fatigue tests inwhich the output of a vibration pick-up mounted on the resonant specimenis used to hold the frequency of a driving motor at resonance;difficulties have been experienced with pick-ups in the past art becauseof their insufcient output.

For a more complete understanding of the invention and for other objectsand advantages thereof, reference should now be had to the followingdescriptions in connection with the accompanying drawings, in which Fig.l is a half-sectional view of my invention for detecting vibrationaldisplacements, connected into a Wheatstone bridge circuit;

Fig. 2 is a view taken along line 2-2 of Fig. 1; Fig. 3 is a view takenalong line 3--3 of Fig. 1; and

` Fig. 4 is a view taken along line 4--4 of Fig. 1.

Numeral I indicates generally a rectangular cross-sectioned housing,closed at each end. Centrally of one side, and projecting inwardly ofsaid housing, is provided a normally projecting cylindrical stub element2. The opposite side is centrally apertured 3 across which are securedtwo tandem spaced flexible plates 4 and 5 which have a sufficiently highnatural frequency to respond to vibrations of a high order. Said platesare centrally apertured to receive assembly screw 6 and are secured tothe housing by sliding their end portions into horizontal receivingslots 1 and 8 and peening said ends secure in said slots.

A cylindrical thrust element 9 is provided consisting of cylindricalsections Ill, II, I2 and I3 which are centrally apertured to receiveassembly screw 6. End section I 3 is threaded to threadedly engage saidscrew 6. An elongated abutment member I4 and a conducting leaf spring I5are likewise centrally apertured to receive assembly screw 6. The abovesaid elements are arranged, assembled and secured to the flexible platesby means of assembly screw 6 in the following order: assembly screw 6,section I0, leaf spring spring I 5, abutment member I4, section II,flexible plate 5, section I2, flexible plate 4, and threaded section I3.Section I3 threadedly engages screw 6 thereby' allowing the screw todraw and secure said assembled elements tightly together and be carriedby said flexible plates. Spring I5 and its abutment I4 are positionedparallel to each other so as to be in juxtaposed relationship throughall deflection of said spring.

Stub element 2 is diametrically bored to receive non-conducting rodularmember I6 which is xed and supported thereby intermediate said rodsends. A ne resistance wire I'I is coiled around one end of said rodularmember I6 in closely wound coils and is then connected into a Wheatstonebridge I8 as one arm thereof. Each individual turn of Wire is insulatedfrom its companion turn. The other end of said rod functions as anabutment for a leaf spring element I9 about to be described. Conductingleaf spring I9 is centrally apertured and secured to the top of stubelement 2, in a position parallel to the axis of coil I'I, by means ofscrew 20 and washer 2|. The stub element 2 projects beyond the receivedrodular element I6 a. distance equal to the thickness of coil I'I sothat the leaf spring i9 secured in position will just overlay theresistance coil I'l tangentially. That part of leaf spring I9 that bearson said resistance coil is surfaced with a metal that has a smallcontact resistance at low contact pressures, thereby making excellentcontact with coil I1.

Said leaf springs I5 and I9 are welded together at their ends 22,generally forming an elliptic spring, and provided with a particularconfigura-- tion such that an approximately linear relationship obtainsbetween the displacement of thrust element 9 and the current or voltagein the indi cator 23 across the bridge I8. Said indicator 23 isresponsive to electrical variations resulting from the association ofleaf spring i9 and resistance coil Il, whereby said congured leaf springchanges the extent of its bearing contact on said resistance coil by achange of the configuration of said spring I 9.

In operation the thrust element 9 is held against any vibrating body tobe investigated. The vibrational displacement cau-ses the springs I5 andI9 to deflect. As leaf spring I9 deects, it changes its configurationand increases-the extent of its bearing contact along coil I 1. Thusprogressively more and more turns are shorted out of the bridge circuitby spring I9, and the bridge is correspondingly unbalanced. Hence, anydeparture from a pre-determined and initial reading or reference point of the milliammeter 23 serves to detect a vibrational displacement. Bysuitable calibration, the milliammeter 23 is made .to indicate straindirectly. When the direction of the vibration is reversed, and the.thrust element reverses its direction correspondingly, more and morecoil windings are progressively "cut-in to the bridge circuit, and thebridge is correspondingly re-balanced.

While I have shown a particular embodiment of my invention, it will beunderstood, of course, that I do not wish to -be limited thereto, sincemany modifications may be made, and I, therefore. contemplate by theappended claims to cover any such modifications as fall within the truespirit and sc'ope of my invention.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. In a. dynamic strain pick-up a housing having an opening in one sidethereof, a flexible means of high natural frequency mountedon thehousing across the opening and adapted to respond to vibrations, athrust membermounted on the flexible means, a resistance coil having asupporting core, mounted in the housing transversely of the thrustmember, and an elliptic spring having an electrical conducting leaf anda non-conducting leaf, the latter being secured to the thrust member andthe former bearing on the resistance coil and adapted to deilectablyextend its bearing contact along the coil to vary the current passingtherethrough as a function of the displacement of the thrust member.

2. In a dynamic strain pick-up a housing having an opening in one sidethereof; a thrust member exibly mounted to operate through said openingand adapted to respond to vibrations:

' resistance coil means mounted in said housing:

and' conducting elliptic spring means having the bottom of said springmeans secured to said thrust member and the top of said spring meanssecurely bearing on said resistance' means and adapted to deflectablyextend its bearing contact along said resistance in a linear relation tothe displacement of said thrust member.

3. A dynamic strain pick-up including a housing having an opening in oneside thereof, a exii REFERENCES CITED The following references are ofrecord in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,759,967 'I'homas May 27, 19301,760,092 Thomas May 27, 1930 2,071,256 Dobbs Feb. 16, 1937 2,305,267Minor Dec. 15, 1942 2,359,245 Ritzmann Sept. 26, 1944 FOREIGN PATENTSNumber Country Date 82,335 Switzerland Sept. 16, 1919

